In endoscopic surgery, a cannula is used to maintain an open passage into a body cavity for introducing surgical instruments into a surgical site. Typically, the body cavity is pressurized with a fluid (such as sterile liquids or gases), which also can be provided via the cannula, to expand the cavity, facilitate maneuverability of the surgical instruments, and to maintain a clear field of view for the surgeon. Soft tissue adjacent the cavity may swell as the tissue absorbs fluid. The cannula also maintains the passage to facilitate surgical instrument insertion and removal.
One problem that has existed with prior cannulas is that they may be partially or completely dislodged from the patient as the instruments are manipulated or exchanged via the cannula, particularly during instability surgery involving loose or thin capsular tissue. If the cannula is partially or completely pulled out of the patient, the body cavity may collapse or fill with fluid or blood, the surgeon loses sight of and access to the cavity, and the surgical procedure is interrupted while the portal into the body cavity is reestablished. During this time, for cavity distention with sterile liquids, the soft tissue can continue to absorb fluid and soften, making it difficult to reinsert the cannula and leading to an increased risk of surgical complications. While different techniques have been employed to improve cannulas and their ability to remain in place during surgery, we believe that further improvements are warranted.